THE CfA REDSHIFT SURVEY

The CfA Redshift Survey was started in 1977 by Marc Davis, John Huchra,
Dave Latham and John Tonry. The First CfA Survey, completed in 1982,
(Huchra, Davis, Latham and Tonry, 1983, ApJS 52, 89) had as its goal
the measurement of radial velocities for all galaxies brighter than
14.5 and at high galactic latitude in the merged catalogs of
Zwicky and Nilson (the UGC). This survey produce the first large
area and moderately deep maps of large scale structure in the nearby
universe, as well as the first crude but truly quantitative measurements
of the 3-D clustering properties of galaxies.
Redshifts are the simplest link to determine galaxy distances.
A description of the redshift is given here
THE REDSHIFT . Basically, since in most places outside
the cores of galaxy clusters or in the very, very local Universe
(the Local Group of Galaxies), the expansion of the universe,
commonly called the Hubble Flow, is smooth, redshift is a surrogate
for distance:

Distance = velocity/(Hubble's Constant) = V/H0

So the measurment of a galaxy's redshift givers you an estimate
of that galaxy's distance --- thus allowing astronomers to map the nearby
Universe.

The second CfA survey (CfA2) was started by John Huchra and Margaret
Geller in the winter of 1984/5. Between 1985 and 1995, we and our students
and co-workers measured relative distances via redshifts for
about 18,000 bright galaxies in the northern sky.

The CfA Survey Data.

Here's a plot of the sky distribution of
the galaxies in the CfA Redshift Survey (J. Huchra and M. Geller 1998).
Each point represents a galaxy in the
northern celestial hemisphere that is brighter than an apparent
blue magnitude of 15.5 and with a measured redshift inside 15,000 km/s.
The nearest galaxies are shown in red, followed by blue, magenta, cyan
and green.

Red V < 3000 km/s

Blue 3000 < V < 6000 km/s

Magenta 6000 < V < 9000 km/s

Cyan 9000 < V < 12000 km/s

Green 12000 < V km/s

The large read area at the center of the map (12 hours, +10 degrees) is
the dense central region of the Virgo Cluster of galaxies which is the
core of the Local Supercluster (see below).
The dark blue points which dominate the RHS of the map (0-4 hours +30 to +40 degrees)
show the location of the
Pisces-Perseus Supercluster, which has been well studied by Giovanelli & Haynes.
The cyan points at 15 hours running almost from the equator to +40 degrees
declination are the Hercules Supercluster studied by Pauline Barmby and myself.
The blank areas running mor eor less north-south and looping over the north celestial
pole are the regions of the sky inaccessible to optical surveys due to dust extinction
when looking through the Milky Way, aka the "Zone of Avoidance." (see 2MASS for how to
fix this!)

The first slice of the CfA Survey.

Redshift surveys are ways
of mapping the distribution of galaxies around us. We use redshift as the
measure of the radial coordinate in a spherical coordinate system centered
on the Milky Way. Below is the "slice of the Universe" that represents
the first set of observations done for the CfA Redshift Survey in 1985 by
Valerie de Lapparent, Margaret Geller and myself. These are spectroscopic
observations of about 1100 galaxies in a strip on the sky 6 degrees wide
and about 130 degrees long. We are at the apex of the
wedge. The radial coordinate is redshift, measured in kilometers per second,
with the current best conversion (see ``Hubble Constant'' below) of about
20 kilometers per second per million light years. That means the outer
arc of the plot is at a distance of about 700 million light years. The
angular coordinate is the right ascension, or the celestial equivalent
of longitude.

This initial map was quite surprising, showing that the distribution of galaxies
in space was anything but random, with galaxies actually appearing to
be distributed on surfaces, almost bubble like, surrounding large empty
regions, or ``voids.'' You can get a clean postscript version of this
figure here . If you use this or any other
image from this site, please credit the Smithsonian Astrophysical
Observatory and the appropriate authors.

Here's the map with six contiguous 6 degree slices in the northern galactic
cap. The structure running all the way across between 8 hours and
17 hours RA and 5,000 and 10,000 km/s is called the ``Great Wall,''
perhaps the largest single structure yet detected in any redshift survey.
Its dimensions are about 600x250x30 million light years, sort of like
a giant quilt of galaxies across the sky. (see Geller and Huchra 1989,
Science 246, 897.)

The Great Wall itself can be viewed in this simple planar projection
of all galaxies in the CfA Survey with velocities between 6,500 and 11,500
km/s in the north galactic cap. Galaxies with velocities between
6,500 and 8,500 km/s are plotted as red points and those between 8,500
and 11,500 are blue. Because the Great Wall is slightly tilted in velocity
space (see the previous figure), the higher velocity end dominates the eastern
portion of the figure. The Great Wall is a surface that has, as
expected, considerable two-dimensional structure --- embedded clusters
and groups of galaxies as well as some filaments and other, more amorphous
structures - basically both low and high density regions (see, for example, Ramella,
Geller and Huchra ApJ 384, 404, 1992). The Coma Cluster is the dense region
right near the center of the plot (13h and +29d).

The redshift distribution of the CfA2 survey can also be seen in this polar
projection of the redshifts for all the galaxies in the CfA2 survey out
to 12,000 km/s. This is a section of a cylinder in equatorial coordinates
looking down from the north pole to the equator with a height of 12,000
km/s and a radius of 12,000 km/s. Tha major structures seen are again
the Local Superluster just above the middle of the plot, the Great Wall
cutting from 9 hours and 5,500 km/s to 15 hours and 9,000 km/s
and the Pisces-Perseus supercluster centered around 1 hor and 4,000 km/s.
The geometry of this projection is similar to that of a hockey puck.

The combination of several new surveys also provides a new view of the
Local Supercluster. The above plot shows the all-sky distribution of
all the galaxies in ZCAT with heliocentric velocities less than 3000 km/s.
This set is essentially made up of objects fromt he CfA Survey in the north,
the SSRS2 survey in the south, the ORS survey in regions not covered by the
others plus the IRAS 1.2-Jy survey all over, especially at low galactic
latitudes (the small points sprinkled throughout the map). Despite the
poor coverage at low galactic latitudes, the LSC and the
central regions around its core, the Virgo Cluster, stand out quite
dramatically.

To give you some idea of the statistical characteristics of the CfA2 catalog,
these two plots show the count statistics (log N - log S) and the V/Vm statitics
for the CfA2 catalog above |b| = 30 degrees log(n)-log(s) ,
V/Vm . For a uniform distribution in Euclidean space,
V/Vm shoul ve 0.50. These plots show first, an excess of brighter galaxies
relative to a normalization at m_pg=13.5, which has long been associated with the
presence of the local supercluster, and second, an apparent slight excess below
15th magnitude that may be associated with the Great Wall. Note that the plots are both
integral statistics (its difficult to define V/Vm for differential counts!)
Part of the excess at faint magnitudes may also be due to nonlinearities in
the Zwicky-Nilson magnitude scale (e.g. Huchra 1976, AJ 81, 952 and many following
references). The luminosity function for the catalog (a measure of the selection
function), calculated using the simple V/Vm method (Schmidt 1968; Huchra & Sargent 1973),
is given in log phi , where phi is the number density
of galaxies per luminosity interval, i.e. the number of galaxies per magnitude
interval per cubic Megaparsec. This is computed for a an area of the
sky given by the boundaries (0-90d, 8h-17h, -2.5-90d, 20h-4h), which covers 36.15% of the
sky, and assumes a Virgo infall of 250 km/s, H_0=75 km/s/Mpc, and an extinction correction
of 0.15csc(b). There are 13,977 galaxies in this subset catalog.

Here is a link to the CfA Redshift Catalog description:
ZCAT DESCRIPTION. You can
access the CfA Redshift Survey data data at this website.
The main ZCAT2000 catalog can ve downloaded here:

It is necessary to download the file via ftp because of its
size. There is a README file describing the data stored there available
for public use, sources for redshifts etc. and information about how
to reference these if you do use them. The compressed public version
of the CfA Redshift Catalogue is in "velocity.dat.gz". There are also
files for the CfA1 survey data (cfa1.dat), the published CfA2 slices,
and subdirectories for the IRAS 1.2 Jy sample, the UZC,
the ORS and many other available redshift surveys.

Some of the small catalogs can be downloaded directly from the web. These
are:

The last update of this file is from April 20 of 2005.
Questions about sources should be addressed to J. Huchra. If you have published a paper
or database that is *not* in our list, please let me know wo we can include it!

Finally, here is a partial list of the template stars and galaxies we use for velocity checks
and studies:

Nowadays, most of the actual templates used are synthetic and can be obtained from
Doug Mink or Mike Kurtz of the SAO Telescope Data Center.

If you have questions about the use
of the Catalogue or anything else here please contact me at
the e-mail address below. I won't promise a prompt response but I will
promise a curteous one! Nathalie Martimbeu (nmartimb@cfa.harvard.edu) is also
responsible for corrections and information, and, if you don't get me
try her.